Hydraulic exercise machines such as illustrated in U.S. Pat. Nos. 4,496,147; 4,480,832; 4,465,274; 4,363,481; 4,063,726; 3,702,188; 3,606,318; 3,530,766; 3,529,474; 3,128,094; and 2,079,594 have found favor because of the reliability inherent in hydraulic energy absorption systems. Especially with respect to exercise stairs, three kinds of hydraulic stair systems have evolved. First, piston cylinder systems have been provided that offer hydraulic step height adjustment through a hydraulic bypass system described in U.S. Pat. No. 4,681,316. Secondly, hydraulic shock absorber based systems are used that are less expensive than piston cylinder systems but offer no step height adjustment, rate control, or the long life features of the piston cylinder systems. Thirdly, ram cylinder systems provide the cost advantages of the shock absorber base systems, and offer the rate control of the piston cylinder systems, but provide no step height adjustment.
By way of definition, hydraulic piston cylinder systems utilize a plug, called a piston, that moves within the cylinder when fluid under pressure is introduced into one end of the cylinder. The universal aspect of a piston is that it seals to the inside walls of a cylinder. As a result, the piston divides a cylinder into two distinct, isolated chambers. A piston rod is normally attached to the piston and extends through one of the two closed ends of the cylinder.
Hydraulic ram cylinders are differentiated from piston cylinders by the absence of a piston. As a result, there is but one chamber associated with the system. A portion of the rod or ram extends into the chamber, and its end provides a surface for the fluid to push against. When fluid is introduced into this chamber, the ram is forced out of the cylinder. Rams can only push; they cannot pull.
Such a ram cylinder system is described in U.S. Pat. No. 4,496,147, issued to Richard J. DeCloux in which steps are phased relative one to the other by the ram cylinder system. Here fluid goes from one ram cylinder to another through a valve which controls the rate of exercise. In one embodiment the steps are attached to pivoted lever arms with linkages between the arms coupled to respective rams. This system, while providing a useful exercise device is not provided with a simple way of adjusting step height.
In U.S. patent application No. 462,835, filed Jan. 10, 1990 by Richard J. DeCloux and incorporated herein by reference, an auxiliary cylinder provides fluid to a ram cylinder system, or removes fluid from the system to adjust the step height. The auxiliary cylinder in one embodiment has a ram which is moved into and out of the cylinder to add or subtract fluid for step height adjustment.
Step height adjustment is in fact important with respect to the comfort of the exercise routine, and it is for this reason that the aforementioned U.S. Pat. No. 4,681,316 was provided with a hydraulic bypass system. However in the implementation of such a piston-type bypass system, as many as twenty separate parts were proven to be necessary in order to implement step phasing and adjustment, rate control, and heat dissipation for a stair climber-type exercise. The result is not only cost and complexity, but also the number of individual separate parts provides avenues for failure. Moreover since each of the pistons was pivotally attached to an arm of the device, all pistons and cylinders had to be flexibly mounted so they could move during exercise.